We characterized a novel gene, AmphiCaBP-like, encoding a putative Ca(2 + )-binding protein (CaBP) with three EF-hand motifs from amphioxus (Branchiostoma belcheri tsingtauense). It exhibits significant similarities with the calmodulin and troponin C proteins from other species. Results of phylogenetic analysis indicated that amphioxus AmphiCaBP-like falls on the base of the troponin C clade. It may be a novel member of the calmodulin-like subfamily. In situ hybridization and RT-PCR analysis showed that AmphiCaBP-like is expressed throughout early development except the stages around the blastula. From neurula stage onward, transcripts of the AmphiCaBP-like are detected in the neural plate, the neural tube, the differentiating somites and the splanchnopleure, as well as the epithelium of the pharynx and gut. It is also expressed in the presumptive, but not the well-developed notochord. In adult amphioxus, the transcripts are found in the epithelial cells of the gut and midgut diverticulus, the wall of coelom, the branchia, the neural cord and gonads.